Displacement engine especially for dental use

ABSTRACT

A DISPLACEMENT ENGINE HAS A CYLINDER WITH AN AXIS. THE CYLINDER IS CLOSED AT ONE END AND MOUNTS A HOLLOW SHAFT ROTATABLE ON THE AXIS AS A CENTER AND HELD AGAINST DISPLACEMENT ALONG THE AXIS. A PISTON IS RECIPROCABLE IN THE CYLINDER AND ALONG THE SHAFT BY MEANS OF A SLEEVE CAM SURFACE AT ONE END REMOTE FROM THE CLOSED END OF THE CYLINDER AND ENGAGING A CAM FOLLOWER EXTENDING RADIALLY FROM THE SHAFT. PRESSURE FLUID IS ADMITTED TO THE CYLINDER ADJACENT THE CLOSED END. AN EXHAUST PORT OPEN THROUGH THE SHAFT WALL BETWEEN THE PISTON AND THE CLOSED CYLINDER END IS ALTERNATELY OPENED AND CLOSED AS THE SHAFT ROTATES BY MEANS OF AN ARCUATE VALVE WALL FAST ON THE PISTON.

sept, 21, 1971 L. P. FLATLAND DISPLACEMENT ENGINE ESPECIALLY FOR DENTAL USE Filed Oct. 17. v 1969 5 Sheets-Sheet 1 l v v wwf/vrai d Lora 7? Enna/v0' i 3f Y QZ/f Y rrolNi/f Y sept. 21, 1971 1 P. FLATLAND DISPLACEMENT ENGINEVESPECIALLY FOR DENTAL USE Filed OG.. 17, 1969 5 Sheets-Sheet n@ www, s l .f 1 11-51-11-- mw NN wx d, JS. n\\\ MN@ rrvPA/Ef Sept. 21, 1971 L, P. FLATLAND DISPLACEMENT ENGINE ESPECIALLY FOR DENTAL USE Filed Oct. 17, 1969 5 Sheets-Sheet 3 wvl/vra? Loro P. FLArL/vv om W #fraz/vir.;

SPt 2l 1971 L. P. FLATLAND DISPMCEHENT ENGINE ESPECIALLY FOR DENTAL USE Filed 061'.. 17,` 1969 5 Sheets-Sheet 4L /M/iA/rdi Lam P. Farrar/v0 MAZ/W Arroz/via QLI' LIV

Sept. 2l, 1971 L. P. FLATLAND n DISPLAC ENGINE ESPECIALLY FOR DENTAL USE Filed Oct. 17, 1969 5 Sheets-Sheet 5 Si j Avn/INTO? Larp P. Enza/v0 .Zr

ozezjf W42 vivir/5 United States Patent Office 3,606,684 Patented Sept. 21, 1971 3,606,684 DISPLACEMENT ENGINE ESPECIALLY FOR DENTAL USE Lloyd P. Flatland, 15 Quisisana Drive, Kentfield, Calif. 94904 Filed Oct. 17, 1969 ,Ser. No. 867,267

Int. Cl. A61c 1/08 n U.S. Cl. 32-26 7 Claims ABSTRACT F THE DISCLOSURE A displacement engine has a cylinder with an axis. The cylinder is closed at one end and mounts a hollow shaft rotatable on the axis as a center and held against displacement along the axis. A piston is reciprocable in the cylinder and along the shaft by means of a sleeve cam surface at one end remote from the closed end of the cylinder and engaging a cam follower extending radially from the shaft. Pressure fluid is admitted to the cylinder adjacent the closed end. An exhaust port open through the shaft wall between the piston and the closed cylinder end is alternately opened and closed as the shaft rotates by means of an arcuate valve wall fast on the piston.

In many fields, particularly in the field of hand-held rotating dental instruments, there is a substantial demand for an improved driving mechanism. Dental hand pieces have been rotated by mechanical means and more recently by very high speed air turbines. There are instances in which the relatively high turbine speed is not essential but substantial torque at relatively low speeds is helpful although diflicult if not impossible to obtain by turbine drive.

It is therefore an object of the invention to provide a displacement engine, particularly for dental use, Which will operate on a pressure fluid, for example compressed air, and will afford adequate rotational speed for most uses and will have relatively high torque at relatively low speeds.

Another object of the invention is to provide a displacement engine especially for dental use which can easily be held in the users hand and will occupy about the same volume as hand pieces now customarily utilized.

Another object of the invention is to provide a displacement engine which will readily start and stop under the control of the operator and will assume intermediate speeds under his control.

A further object of the invention is to provide a displacement engine having a relatively long life and proreadily available for use.

An additional object of the invention is to provide a displacement engine which affords, in most embodiments, a relatively even turning moment.

A still further object of the invention is to provide a displacement engine which is quiet and vibration free.

A further object of the invention is to provide a displacement engine in which the parts, even in relatively small sizes, can be accurately and consistently manufactured.

A further obiect of the invention is to provide a displacement engine having a relatively long life and prolonged consistent performance.

A further object of the invention is in general to provide an improved displacement engine.

Other objects together with the foregoing are attained in the embodiments of the engine described in the accompanying description and illustrated in the accompanying drawings, in which:

FIG. 1 is inclusive of three diagrammatic views, the

center one being a cross-section on an axial plane through a form of engine pursuant to the invention in one operating position, and the end views being timing diagram illustrations in transverse cross-section through valve ports;

FIG. 2 is a view like FIG. 1 but showing the parts in a position ninety degrees after the position shown in FIG. 1;

FIG. 3 is a view comparable to the preceding figures but showing the parts in position ninety degrees after the position of FIG. 2;

FIG. 4 is a view like the preceding figures but showing the parts in a position ninety degrees after the position of FIG. y3;

FIG. 5 is a cross-section to an enlarged scale through the axis of an actual engine constructed pursuant to the invention, parts of the structure being broken away to reduce the size of the drawing;

FIG. 6 is a continuation of the structure shown in FIG. 5, the view being in cross-section on an axial plane;

FIG. 7 is a cross-section on an axial plane through a single-piston, alternate form of the displacement engine;

FIG. 8 is a cross-section on an axial plane through a further modified form of displacement engine;

FIG. 9 is a detail showing in side elevation of modified form of piston-and cam construction;

FIG. 10 is a view to an enlarged scale showing in developed form the contour of the piston cam surface shown in FIG. 9;

FIG. 11 is a view similar to FIG. `8 but showing a different form of reversing arrangement;

FIG. 12 is a cross-section to an enlarged scale, the plane of section being indicated by the line 12-12 of FIG. 1l;

FIG. 13 is a cross-section like FIG. l2 but indicated by the line 13-13` of FIG. ll;

FIG. 14 is a cross-section like FIG. 12 but indicated by the line 14-14 of FIG. 11;

FIG. 15 is a view similar to FIG. `8 but showing, partially diagrammatically, a different form of means for precluding piston rotation; and

FIG. 16 is a cross-section, the plane of which is indicated bythe line 1=616 of FIG. 15.

The displacement engine in any of its embodiments pursuant to the invention has certain characteristics making it suitable for use in a widely different number of e11- vironments, but it is especially useful in and has been illustrated as it is embodied for use in the field of dental instruments such as a hand piece designed to drive any of various dental tools.

Furthermore, while the engine in its various modifications Will operate on any appropriate fluid which can flow from a source of relatively high pressure to a sink of relatively low pressure it has conveniently been embodied to operate on compressed atmospheric air containing some finely divided lubricant therein, the air being at a pressure of, say, fty pounds per square inch initial pressure and discharging to atmospheric pressure, as an example.

For purposes of explanation attention is first directed to FIGS. 1-4 inclusive which, although diagrammatic, illustrate the cycling of the displacement engine and for clarity omit some of the details of actual construction.

The engine includes a right, circular cylinder 6 symmetrical about a longitudinal axis 7. The cylinder 6 is substantially closed at an inlet or head end 8 except for an inlet duct l9 leading to a source 11 of appropriate fluid under pressure. At the other end the cylinder 6I not necessarily but conveniently is substantially closed by a wall 12 except that there is provided an outlet duct L3 leading to a sirrk 14 at a pressure lower than the source 11. Designed to rotate about the axis 7 and to be constrained against any axial movement with respect to the cylinder 6 is a through shaft 16. The shaft is appropriately supported and conned and can extend from one or both ends of the cylinder. The shaft is for the most part solid in this showing.

` Designed to reciprocate within the cylinder 6 is a primary piston 21 fitting the cylinder well and having a transverse, planar top or head surface 22 at its end nearest the head 8. The piston 21 has a sleeve cam surface 23 at its opposite end, remote from the head 8. The cam surface 23 is conveniently and approximately or actually defined by a plane extending obliquely to the axis 7. Arranged to abut the planar, oblique cam surface 23 is a cam follower 24 including a stub shaft 26 extending radially from and -fixed on the shaft 16. In some instances the follower includes an anti-friction roller 27 directly in contact with the cam surface.

To confine the piston to rectilinear translation, that is, to preclude rotation thereof relative to the cylinder 6 and for other reasons the piston` is provided with a transverse, axially extending valve wall 28 which is substantially planar and defines the margins of a partial sleeve 29 partly encompassing the shaft 16. Abutting the wall 28 on both sides of the axis are restraining pins 31 and 32 on which the sleeve margins are slidable and preclude the forbidden piston rotation.

At an appropriate point in the periph-ery of the shaft 116 there is a radial port 36, usually made circular in crosssection which communicates with a central bore 37 making this part of the shaft hollow. The bore 37 extends axially along the shaft but is blocked by a transverse barrier 318. Below the piston and above the barrier, the bore '37 opens through a second port 39 likewise circular in cross-section, into the cylinder.

With this arrangement there is a primary inlet chamber 41 defined within the cylinder above the piston and a secondary or intermediate chamber 42 defined within the cylinder belo-w the piston. Likewise provided is a tertiary chamber 43 separated from the chamber 42 by a secondary piston 44 substantially identical with the primary piston 21. The piston 44 has a cam surface 46 comparable to the surface 23 and in the same polar orientation with respect to the cylinder 6. The secondary piston operates with a cam follower 47 having a stub arm 48 extending radially from the shaft 16 but polarly displaced one-hundredeighty degrees from or out of phase with the stub shaft 26. The piston 44 has a valve sleeve 49 with a transverse surface 51 like the wall surface 28 engaged by a pair of pins 52 and 53 stationary in the cylinder. In this fashion the secondary piston is allowed to reciprocate but is prevented from rotation.

The interior of the shaft 16 is bored out to provide a chamber 56 below the plug 318 and a port 57 like the port 36 is provided through the shaft wall between the chamber 56 and the cylinder but the port 57 is displaced polarly one-hundred-eighty degrees from the port 36. At a convenient location an outlet port 58 opens from the charnber 56 into the tertiary chamber 43.

With the parts in position as shown in FIG. l, the shaft 16 is intended to rotate in the direction of the arrow 61. The primary chamber 41 has just been sealed by closure of the port 36 and remains sealed except for the always open supply duct 9. The secondary chamber 42 and the tertiary chamber 43 are both open to the low pressure exhaust 14 because the port 58 is always open and the port 57 is just about to open. Thus, there is a relatively high pressure on the head of the piston 21 and a low pressure beneath the piston 21 so that the piston tends to be driven away from the head 8 by the pressure difference. The cam face 23, bearing upon the follower 27, causes further rotation of the shaft 16 after the shaft has moved slightly past the upper dead center position illustrated. l

As the piston 21 is driven away from the head 8 it rotates the shaft 16 for a quarter turn into the position shown in FIG. 2. The port 36 is still blocked by the valve sleeve 29 and the other ports remain as previously described. The motion of the piston 21 continues down- 36 has rotated with the shaft 16 until it begins to emerge from the barrier provided by the valve sleeve 29. Thisl permits the pressure fluid within the primary chamber 41 to discharge through the port `36 into the bore 37 to flow along the axis and discharge through the always open port 39 into the secondary chamber 42. At this time the port 57 has rotated into a closed position in which ow through the port is blocked by the valve sleeve 51. Under these conditions pressure lluid from the source flows into and from the primary chamber 41 into the secondary chamber 42 now having a blocked outlet. The pressure in pressure by the piston 21. Movement of the piston 21,

becomes relatively easy since pressure on opposite sides thereof is balanced but the piston 44 exerts full force on the shaft 16. As the shaft turns the piston 44 continues away from the head 8 into the position illustrated in FIG.

4. This is ninety degrees later than the F'IG. 3 position. The port 57 is still closed to trap pressure fluid within the secondary chamber 42 while the low pressure continues beneath the piston 44. During this time the rotation of the shaft has caused the follower roller 27 to cam against the surface 23 on the piston 21 and to drive the piston toward the head 8 during which operation the port 36 has remained open.

During the next ninety degrees of rotation of the shaft the parts travel from the position shown in FlG. 4 and return to the position shown in `FIG. 1. At that time the port 57 resumes the about to open position shown in FIG. 1 so that the pressure within the secondary chamber 42 and within the tertiary chamber 43 shortly drops to the exhaust value. At the same time the valve port 36 returns to its FIG. 1 position in which it is blanked by the valve sleeve wall 29. Pressure uid from the source can no longer leave the primary chamber 41. The pressure therein persists at the high value whereas the pressure beneath the piston in the secondary chamber 42 resumes the low value. The force is then on the primary piston 211 to move away from the head 8, as before, during which motion of the shaft 16 the follower 47 restores the piston 44 to its former position.

With this Vmechanism the pressure fluid displaces the two pistons within the cylinder in cyclic paths to impart two successive driving torques to the shaft for each shaft rotation. While there are two dead center positions with this two piston mechanism and while occasionally the mechanism must be externally started, continued rotation is readily accomplished because the moving parts have suffi- Y cient momentum to act a a fly wheel. For illustration herein, the timing of the various events is presumed to take place instantaneously and exactly at the locations indioretical concept and the port size, both circumferentially and axially, is also varied. Sometimes the port area especially during cylinder exhaust is partially restricted to retain some pressure on the piston to hold the cam in contact with the follower when a unidirectional cam is used. The timing of the events also varies with the amount of air to be used, with the designed speed range of theshaft and to allow for tolerances in manufacture and wear of the parts.

In practice there is some slight leakage not only through the various covered ports but also past the pistons. This is I a small amount and instead of being considered detrimental is advantageous in that it affords an air bearing between the relatively moving parts. The air bearings reduce and may eliminate the lubricant, such as oil, that usually is introduced with the propulsive fiuid. In any event a displacement engine, as described, is effective to utilize the force of a pressure fluid to afford a satisfactory rotation of a driven shaft, the parts being quite simple and being arranged in such a fashion that the shape or envelope of the resulting structure lends itself to many uses and particularly to incorporation in a dental handpiece.

An actual, operating form of a displacement engine driven dental handpiece is illustrated in FIGS. and 6. Therein a metal cylinder 71 is symmetrical about an axis 72 and at one end has threads 73 on which a head cap 74 is screwed. The head cap is flanged partially to confine an aperture head fitting 76 into which a fiexible supply tube 77 extends. The tube 77 extends to a source 78 of fluid under pressure. The Ifitting 76 is not only confined by the cap 74 but is likewise axially located by a head plug 79 fixed within the cylinder 71 and formed with a through passage 81. A bearing 82 is fixed within the cylinder 71 and rotatably supports one end of a hollow shaft 83, a retainer 84 holding the bearing against the plug 79. There is a sufficient opening through the bearing 82 to allow fluid from the passage 81 into aprimary chamber 86 between the bearing and a piston 87 reciprocable within the cylinder 71.

The piston 87 represents any one of two or three or more pistons identical with each other and arranged axially apart and within the cylinder. The piston 87 carries a packing ring 88 to reduced leakage and has a cam track 89 adapted to abut a roller bearing 90 on a radial stub shaft 91 fast on the shaft 83. Also the piston 87 carries a valve wall 92 having a valve surface 93 lying in a plane parallel to the axis 72 and, in addition, has a saddle 94 to assist in forming a good bearing for the piston 87 on the shaft. A port 96 in the shaft communicates through a shallow groove 97 and a port 98 with a secondary chamber 99 whenever the port 96 is uncovered.

Successive pistons are similarly arranged but with their ports 96 or their valve surfaces 93 appropriately positioned peripherally of the shaft. That is, if a single piston is utilized then the port 96 has a location with respect to the valve wall 92 and the cam 89 substantially as shown in FIG. 5. If there are two pistons then the valve walls (or ports) are disposed one in the same polar location shown in FIG. 5 and the other at one-hundred-eighty degrees thereto. If there are three pistons then the valve walls 92 or ports) are disposed one as shown in FIG. 5 and the other two at one-hundred-twenty degrees progressively therefrom. Similarly, if there are four pistons then the orientation of one of the valve walls is as shown in FIG. 5 with the successive valve walls at ninety degrees thereto and to each other.

In an arrangement of this sort, particularly one having three or four pistons or more, the closure of each chamber relative to the closure of lthe chamber next in succession following it is preferably of an angular duration of threehundred-sixty degrees divided by the number of pistons. That is, three pistons have a closure duration of onehundred-twenty degrees each, -whereas four pistons have a closure duration of ninety degrees each and so on. The cams, when contoured as shown, have two dead center positions one-hundred-eighty degrees apart (in most instances) but the duration of the effective driving impulse of the related piston is something less than one-hundredeightly degrees. The configuration of the valve wall 92 and the contour of the ports are consequently preferably arranged so that the pressure differential across any piston occurs centrally and symmetrically with respect to the total theoretical stroke. That is, if the theoretical power stroke of the piston extends over one hundred eighty degrees of shaft rotation, then it is preferred to arrange the piston exists at maximum for only one-hundred-twenty degrees of shaft rotation,then it is preferred to arrange the valve wall and exhaust port so that discharge from the chamber above each piston is blocked beginning thirty degrees past top dead center, continues to be blocked for the next one-hundred-twenty degrees and then resumes through the exhaust port at one-hundred-fifty degrees past top dead center. In this way the pressure difference on each piston is most effective when the cam driving mechanism is 4likewise most effective.

Spent pressure fluid is released to the ultimate chamber 101 and fiows through a port 102 into the hollow shaft 83 toward the same end at which it entered. That is, the exhaust fluid travels from the interior of the shaft into a discharge chamber 103 segregated from the primary chamber 86 by a packing Washer 104. Efiiux from the chamber 103 is controlled by a manually adjustable needle valve 106 governing communication to an outlet duct 107 carrying a fibrous muffler 108 to reduce the sound of the discharge to the atmosphere. With this arrangement the operator by adjusting the needle valve 106 can regulate the back pressure and so the volume of fiuid passing through the mechanism and the speed of rotation of the shaft.

At the opposite end the cylinder 71 carries a bearing 116 supporting the other end of the shaft 83, there being a retainer 11`7 to preclude any axial displacement. The bearing is also confined against a tip housing 118 screwed in position and symmetrical about the axis 72. This body carries a tail shaft 119 supported in an auxiliary bearing 121 adjacent a dental chuck 122. A burr 123 or comparable tool can readily be introduced into the chuck 122 for temporary retention and for rotation.

Under some conditions it is desired to reverse the rotation of the tool 123 without reversing the rotation of the engine itself. Under those conditions I provide on the shaft 83 within the housing 118 a bevel gear 126 nonrotatable on the shaft 83 and backed by a collar 127. The shaft 83 has a pilot extension 128 within a bore 129 within the tail shaft 119. A sleeve 131 is freely rotatable on the shaft 83 and carries a number of radial, stub shafts 132 each of which carries a central bevel gear 133 meshing on one side with the bevel gear 126 fast on the shaft 83 and on the other side with a bevel gear 134 fast on the tail shaft 119. Extending from the shaft 119 is a radial collar 136 carrying one or more radial screws 137 urging friction blocks 138 against the shaft extension 128. Under normal conditions of operation the friction load between the shaft 119 and the pilot shaft 128 is sufiicient so that the planetary differential mechanism (the gears 126, 133 and 134) rotates as a body and the shafts both turn together in the same direction.

Means are provided for reversing the tool direction. Movable in a slot 141 cut in the housing 118 is a stop pin 142 connected to a sleeve 143 slidable on the outside of the housing 118. In the retracted position of the sleeve and the pin 142, as shown in FIG. 6, the differential mechanism is not interfered with. However, when the user displaces the sleeve 143 toward the left in FIG. `6 the pin 142 gets into the rotary path of the spindles or stub shafts 132 and precludes further rotation. The shaft 83 continues to rotate the gear 126 which in turn causes the gears 133 to revolve about their stub shafts and to drive the gear 134. This operates the shaft 119 in a sense opposite to that of is previous direction of rotation accompanied by sliding friction between the blocks 138 and the pilot extension 128. When reverse movement is no longer required the user restores the sleeve 143 to its original condition with the stop pin 142 out of the path of the stub shafts 132. The differential mechanism then revolves as a body due to the frictional drag of the blocks 138 and the shafts 83 and 119 resume their rotation together in the same direction.

For most uses it is preferred to have the relatively smooth, uniform operation of an engine with three or more pistons but it is entirely possible for some uses t0 provide a displacement engine in which only one piston is employed. As particularly disclosed in FIG. 7, the arrangement includes an outer cylinder 151 symmetrical about an axis 152 and having a substantial closure 153 at one end. Anti-friction bearings 154 and 156 are situated within the cylinder 151 and support a shaft 157 for rotation about the axis 152. Leading into the cylinder adjacent one end thereof is an inlet duct 158 for uid under pressure..Near the inlet duct 158 within the cylinder and fast on the shaft 157 is a fly wheel 159 having sucient mass under normal conditions to rotate the shaft 157 for several cycles once sufficient energy has been imparted thereto.

The shaft 157 preferably is substantially hollow to afford an inlet passage 161 from a head chamber 162. Defining one end of a primary chamber 163 within the cylinder is a piston 164 having an axial slot 166 cut in one side thereof. A stationary pin 167 anchored in the cylinder 151 projects into the slot 166 and while permitting reciprocation of the piston precludes rotation thereof. The piston has an inclined cam face 168 bearing against an anti-friction bearing 169 journaled on the end of a stub shaft 171 extending radially from and fast on the shaft 157.

A barrier or block 172 within the shaft 157 prevents communication through the shaft but pressure uid can ow from the passage 161 through a port 173 into the primary chamber 163. Outflow from the primary chamber 163 is governed by a port 174 covered and uncovered by the generally planar surface of a partially circular valve wall 177. A saddle 178 affords extra bearing for the piston. Flow through the port 174 is into a shaft passage 176 leading to the atmosphere and, except for the block 172, being a continuation of the passage 161.

.In the operation of this device when pressure fluid is made available through the duct 158 and to the head chamber 162 and the primary chamber 163 the shaft 157 is initially rotated by any suitable means, thus imparting some energy to the ily wheel 159. At an appropriate point in the rotation of the shaft the port 174 is blocked by the valve wall 177 so that a differential pressure on the piston results. This port blocking occurs substantially -when the piston is at its upper dead center position or shortly thereafter. The piston descends under pressure for substantially a half rotation of the shaft not only imparting force to the shaft but also imparting energy to the lly wheel 159. Near bottom dead center the port 174 is opened by rotation of the valve wall 177 so that pressure fluid from the duct 158 flows through the entire device. The piston 164 is then subjected to only a small differential force. Since the shaft then has the momentum of the fly Wheel 159 to keep it turning the follower 169 bears against the cam face 168 and restores the piston 164 to its inner or top dead center position or slightly beyond. The cycle then repeats since substantially at this time the port 174 is reclosed. While this form of the device is not self starting it does operate Well and has the virtue of being simple.

Under some more sophisticated conditions it is desired to provide a structure which starts with high torque, can be reversed and can operate smoothly for protracted times in either direction of rotation. Under those circumstances an arrangement as shown in FIG. 8 is preferred. In this instance there is provided an outer cylinder 181 symmetrical about an axis 182. The cylinder houses bearings 183 and 184 for a through shaft 186 carrying a dental tool chuck 187 near one end. The cylinder near the head end has threads 189 to engage a removable cap 191 which grips the flange 192 of a head plug 193. The plug has a pressure bore 194 therethrough anda discharge bore 196 therein. The latter leads through a duct 197 to a central chamber 198.

Adapted to abut the plug 193 is a head fitting 199 rotatable about the axis 182 relative to the cylinder 181 by means of a bearing 201. A exible tube, not shown, joins a tting 202 seated within a supply passage 203 cornmunicating with the passage 194. Similarly, the passage 204 in the fitting communicated with the passage 196 and carries a Connector 206 either left open to the `atmosphere or preferably carrying a flexible discharge tube (not shown) leading to a convenient discharge point. With this arrangement, when the fitting 199 is in the position shown then the incoming pressure fluid travels through the passage 194 and the discharge uid travels through the passage 196, but when the fitting is rotated a half turn ywith respect to the cylinder 181 then the passage 196 becomes the pressure passage and the passage 194 becomes the exhaust passage. At intermediate locations of the fitting the passages 194 and 196 are variably obstructed and act as throttles.

Surrounding the shaft 186 within the chamber 198 is a seal bushing 207 effective to preclude leakage between the high pressure and low pressure sides of the shaft.

Within the cylinder 181 is a primary chamber 211 partially defined by a piston assembly 212. This includes a pair of piston members 213 and 214 secured together by an encompassing sleeve 216 slidably bearing on the inside of the cylinder. The sleeve 216 has an axially extending slot 217 into which a pin 218 extends. The piston assembly therefore is prevented from rotating but can reciprocate. The piston member 213 has cam surface 219 thereon whereas the piston member 214 has a cam surface 221 thereon. The two surfaces 219 and 221 are complementary and define a closed cam track between them. Within the cam track a follower 222 is disposed on a radial stub shaft 223 fixed on the shaft 186. A channel 226 cut into but not through the shaft affords communication between the primary chamber 211 and a secondary chamber 227 when a valve wall 228 on the piston uncovers the port Within the chamber 211 defined by the end portion of the channel 226.

In a comparable fashion the secondary chamber 227 is separated from a tertiary chamber 229 by a piston assembly 231 having its own channel port 233 and similarly the tertiary chamber 229 is separated from a discharge chamber 234 by a piston assembly 235 just like the piston assemblies 212 and 231. The discharge chamber 234 is always connected through a port 236 to a central passage 237 in the shaft opening to the chamber 198 and so to the discharge connector 206.

With this arrangement the shaft is rotated by oscillation or reciprocation of the pistons and the direction of rotation depends on which side of the piston assembly happens to be at the higher pressure depending on the location of the head tting 199.

With displacement engines 0f the present sort it is not essential that the various cam faces always be symmetrical. It is preferable in some instances to provide an asymmertical cam surface. That construction is shown in FIGS. 9 and l0. In this instance the shaft 238 is as before and so is the main piston body 239 but the cam surface 240 is not symmetrical. As shown in FIG. 10, a symmetrical development of the cam surface is represented by the broken line 241 showing the cam equally contoured on opposite sides of a center line 242. An asymmetrical cam has a steep ramp 243 so that the maximum point 244 is displaced from the line 242. Although the ramp 243 is considerably steeper than before, the complementary ramp 245 is less steep. This means that a stroke of the cam in one direction might involve more than one-hundredeighty degrees rotation of the shaft and in the other direction might involve less than one-hundred-eighty degrees rotation of the shaft.

The arrangement of FIG. 8 is particularly adapted for use with a dental chuck adapted to be positioned in one rotational location when a tool is inserted or removed. The shaft 186 has a reentrant bore 261 adapted to receive a tool stem. A set screw 262 is threaded into the shaft and is frictionally retained by a block 263. The screw preferably has an Allen head accessible to a wrench inserted through an open collar 264 on the tip housing 266 threaded into the cylinder 181. So that the collar 264 and the set screw 262 will be alignment when the tool stops, a conical spring 267 is disposed between the bearing 184 and the adjacent piston assembly 235. When no other forces are exerted, the spring 267 moves the assembly 235 and :the shaft 186 to upper dead center position of the follower 222 at which the set screw is available through the hole of the collar 264.

If the direction of tool operation must be often reversed, an arrangement as shown in FIGS. 11-14 is preferred. Some parts are omitted or are not referred to since they are as before. The construction is quite similar to that shown in FIG. 8 but the pistons 271, 272 and 273 are single acting and the tubular drive shaft 274 extends through the head 276 of the cylinder 277 and carries a thumb wheel 278. A reversing sleeve 279 is telescoped within the shaft 274 and has an end knob 281. A spring pressed detent 282 in the wheel 278 engages either of two opposite depressions 283 in the sleeve 279. The shaft 274 and the sleeve 279 can revolve together but can be put Vand held 180 degrees out of phase with each other.

The primary chamber 286 has a high pressure inlet 287 and has two opposite outlet ports 288 and 289 in the shaft 274. These are opened or blocked by a valve wall 291 on the piston 271 in the usual way. Registering with either one of the ports 288 and 289 is a single exhaust port 292 opening into the sleeve 279 which also has several outlet ports 293 always open through a ring of discharge ports 294 in the shaft 274 into the secondary chamber 296, as before. A plug 297 precludes further flow through this portion of the sleeve. The construction is repeated for the piston 272 and the piston 273 at the bottom of the tertiary chamber 298. Exhaust to the atmosphere is through a duct 299 from the outlet chamber 301.

With the reversing sleeve 279 in one position relative to the shaft 274, as shown in FIG. 1l, the direction of shaft rotation is in one sense, since all of the corresponding ports like port 288 are operable, whereas all of the ports like port 289 are covered and are inoperable. When the reversing sleeve 279 is rotated one-half turn relative the shaft 274, the port 288 and others like it in the chambers 296 and 298 are covered and the opposite ports 289 and those like it in the secondary and tertiary chambers 296 and 298 become operative. The rotational sense of the Shaft 274 is thus reversed.

It is necessary to keep the pistons from rotating within the cylinder and several means are shown for that purpose involving engagement with the cylinder wall. In some cases it is preferred not to involve the cylinder wall nor the piston wall in performing this function. As shown in FIGS. 15 and 16, the construction generally is as previously described but the head end 305 of the cylinder has irregularities 306 engaged by a tting flange 307 of a retainer shell 308 held in place against rotation and translation by a cap 309. The semi-cylindrical retainer shell 308 has diametrically opposed sliding ways 311 and 312.

The primary piston assembly 313 is typical of all the piston assemblies and has an enclosing casing 314 substantially as shown in FIG. 8 except that at one end the casing has an extension 316 on one side to provide sliding ways 317 and 318 abutting the ways 311 and 312. Thus, while the piston assembly 313 can reciprocate freely in the cylinder, there can be no relative rotation therebetween. Comparably, the assembly 313 has an oppositely disposed extension 319 at the other end engaging an extension 321 on the next piston assembly, and so on. The piston asembly nearest the outlet from the cylinder may or may not have an extension engaging a related extension anchored in the outlet end of the cylinder and substantially duplicating the retainer shell 308.

In all of the forms of the invention there is provided a displacement engine particularly adapted for use in a dental handpiece and for operation on compressed air. The engines easily afford a range of speeds from to about 10,000 revolutions a minute. There is afforded high torque starting in either direction and very close and ac- 10 curate speed control with quiet, smooth functioning in a lasting and economical manner.

What is claimed is:

1. A displacement engine especially for dental use comprising a cylinder having an axis and closed at one end, a shaft, means mounting said shaft in said cylinder for rotation about said axis and against displacement along said axis, a piston constrained to reciprocation in said cylinder and along said shaft, means forming a cam surface at the end of said piston opposite said one end, a cam follower in engagement with said surface and fast on said shaft, means for admitting actuating fluid to said cylinder adjacent said one end, means including an exhaust port opening from said shaft into said cylinder adjacent said one end for conducting said fluid from one end of said piston to the other end thereof, and a valve wall on said piston adapted during rotation of said shaft to cover said exhaust port as said piston moves away from said one end and to uncover said port as said piston moves toward said one end.

2. A device as in claim 1 including multiple pistons reciprocable in said cylinder and along said shaft, means forming multiple cam surfaces one adjacent each of said pistons at the end thereof opposite said one end, multiple cam followers each in engagement with a respective one of said cam surfaces, means including multiple exhaust ports opening from said cam surfaces, means including multiple exhaust ports opening from said shaft into said cylinder for conducting said fluid from the corresponding one end of each of said pistons to the corresponding other end thereof, a valve wall on each of said pistons adapted during rotation of said shaft to cover a respective one of said ports as said respective pistons move away from said one end and to uncover said respective one of said ports as said pistons move toward said one end, said ports, said valve walls said cam surfaces and said cam followers associated with each of said pistons being evenly spaced apart around said shaft.

3. A device as in claim 1 including means for precluding relative rotation between said piston and said cylinder.

4. A device as in claim 1 in which said cylinder is of a diameter and length to be readily held in a human hand, a tool-receiving chuck is connected to rotate with said shaft, and said means for admitting actuating fluid is flexible.

5. A device as in claim 1 including means for releasing spent actuating fluid from said cylinder adjacent the other end thereof, and means for alternatively connecting said admitting means or said releasing means to high pressure actuating fluid While simultaneously connecting said releasing means or said admitting means to atmosphere.

6. A device as in claim 1 in which said cam surface has an out-stroke portion of a predetermined length and an in-stroke portion of a dierent length.

7. A device as in claim 1 in which the out-stroke part of said cam surface has portions in unfavorable driving engagement with said cam follower and has an intervening portion in favorable driving engagement with said cam follower and said valve Wall covers said exhaust port only when said can surface has said intervening portion in favorable driving engagement with said cam follower.

References Cited UNITED STATES PATENTS 1,257,753 2/1918 Smith 91-332 2,265,989 12/1941 App 91-232 ROBERT PESHOCK, Primary Examiner U.S. Cl. X.R. 91-232 

